This invention relates to a Bloch-line memory device for memorizing information as a pair of Bloch lines in a magnetic medium.
A conventional Bloch-line memory device comprises a magnetic medium having a principal surface and an easy axis of magnetization that is orthogonal to the principal surface. The magnetic medium comprises at least one magnetic domain of an elongated ring shape that is defined between inner and outer domain walls orthogonal to the principal surface. The outer domain wall is for memorizing an information signal as a pair of Bloch lines which are orthogonal to the principal surface. Such a Bloch-line memory device is disclosed, for example, in U.S. Pat. No. 4,583,200 issued to Susumu Konishi and the present applicant.
Another conventional Bloch-line memory device is disclosed, for example, in U.S. Pat. No. 4,731,752 issued to Yasuharu Hidaka, the present applicant. In the Hidaka Bloch-line memory device, the magnetic medium has a first groove or stepped portion which has a first groove or step depth from the principal surface to a bottom surface of the first groove to leave a portion of the principal surface as a plateau with the plateau extended in a predetermined direction. The plateau has first and second plateau end portions spaced apart in the predetermined direction and a plateau intermediate portion between the first and the second plateau end portions.
A magnetic domain generator controllably generates the magnetic domain between the inner and the outer domain walls. The inner domain wall surrounds the plateau and is extended from the bottom surface of the first groove orthogonally of the principal surface into the magnetic medium. On generating the magnetic domain by using the magnetic domain generator, presence of the first groove enables the inner domain wall to locate near to the plateau. This renders the magnetic domain stably. In other words, the inner domain wall exactly surrounds the plateau.
In Japanese Unexamined Patent Prepublication or Kokai No. Syo 63-255,894, namely, 255,894/1988, a different Bloch-line memory device is disclosed by the present applicant and three others. As will later be described in conjunction with one figure of the accompanying drawing, the magnetic medium further has a pair of second grooves and a third groove. The second grooves are extended in the predetermined direction on both sides of the plateau and share a second depth which is deeper than the first depth. The third groove has the second depth and is contiguous to the second grooves. The third groove comprises first and second groove portions which are parallel to and orthogonal to the predetermined direction. The second plateau end portion is nearer to the third groove than the first plateau end portion.
The magnetic domain generator generates the magnetic domain having the inner and the outer domain wall. The inner domain wall surrounds the plateau like in the Hidaka Bloch-line memory device. The outer domain wall surrounds the plateau and is extended from the bottom surface of the first groove orthogonally of the principal surface into the magnetic medium. Presence of the second grooves enables the outer domain wall to locate near to the plateau on making the magnetic domain generator generate the magnetic domain.
The Hidaka et al Bloch-line memory device is, however, defective in that the magnetic domain can not stably have a portion of the elongated ring shape near the second plateau end portion under the influence of the second groove for the reason which will later be described.